Explosive cladding on geometrically non-uniform metal material

ABSTRACT

A method for explosively cladding one metal having a non-linear surface on another metal having a similar non-linear surface. A metal base member is spaced from a metal cladding plate an an explosive is positioned over the cladding plate whereby ignition of the explosive forces the cladding against the metal base to create a metallurgical bond.

United States Patent [191 Chang [451 Apr. 24, 1973 [5 1 EXPLOSIVECLADDING 0N 3,140,539 7/1964 Holtzman ..29 421 E x GEOMETRICALLYNON-UNIFORM 3,263,323 8/1966 Moher et al... ....29/421 E X MET MATERIAL3,364,562 l/l968 Armstrong ..29/470.l 3,377,694 4/1968 Simons et a1.....29/421 E X [75] Inventor: Kyung Taik Chang, Seoul, South 3,419,9511/1969 Carlson ..29/497.5 X Korea 3,434,197 3/1969 Davenport ..29/470.l

3,535,767 10 1970 D h J l ..29 470. [73] Assignee: Korea Institute ofScience and l 0 any r at a l 1 Technology Seoul south Korea 1 PrimaryExaminer-J. Spencer Overholser [22] F iled: Jan. 22, 1971 AssistantExaminerRonald .1. Shore [30] Foreign Application Priority Data Jan. 24,1970 Korea 122/70 [52] US. Cl ..29/470.1 [51 Int. Cl. ..B23k 21/00 [58]Field of Search ..29/421 E, 470.1, 29/486, 497.5

[56] References Cited UNITED STATES PATENTS 3,140,537 7/1964 Popoff..29/497.5 X

DETONATOR Attorney-Finnegan, Henderson & Farabow [5 7 1 ABSTRACT Amethod for explosively cladding one metal having a non-linear surface onanother metal having a similar non-linear surface. A metal base memberis spaced from a metal cladding plate an an explosive is positioned overthe cladding plate whereby ignition of the explosive forces the claddingagainst the metal base to create a metallurgical bond.

10 Claims, 6 Drawing Figures EXPLOSIVE BUFFER MATERIAL CLADDING SPACE RS6 DlSTANCE BASE METAL Patented, Apr-i124, 1973 I. 3,728,780

3 Sheets-Sheet 3 Ellie!!! W ATTACHED SHOCK WAVES RELEASE AT, THECOLLISION POINT V Y ISONIC VELOCITY) D iliillil F/6.-3b /l 'd,/-,///////////////A SHOCK WAVES P H613 \@+%JET HIGH VELOCITY JETEMANATING THE COLLISION POINT INVENTOB KYUNG T. CHANG n E9011,flrzJevsoa 8' 701050111 ATTORNEYS EXPLOSIVE CLADDING ON GEOMETRICALLYNON-UNIFORM METAL MATERIAL This invention relates to the cladding ofmetals upon other metals, and more particularly to a method of claddingone metal upon another by means of explosives.

In factories and plants many facilities are operated in variouscorrosive environments. As a result, the surfaces of these facilitiesmust be clad with corrosive resistant metals. For example, containers,tanks and conduits of chemical plants or pharmaceutical plants are cladinside with either stainless steel, titanium alloy, lead or the like,for these cladding materials can withstand an acidic or alkalinecorrosive environment. In general, corrosion-resisting metal is moreexpensive than corrodible metal, and to prevent the latter metal frombeing corroded, the portion of the metal exposed to and in contact withcorrosives should be clad with corrosion-resisting metal in anappropriate thickness.

Cladding on metallic surfaces has been made by various methods, such asmetalizing process, electrolytical or electrochemical deposition, andmechanical forming by rolling or other means of distortion.

The aforesaid methods heretofore employed for cladding one metal uponanother have generally served the purpose but have not been satisfactoryunder all conditions of service. For example, the aforementioned methodsare usually carried out by dipping the base metal into the moltencladding material. This necessitates close controls of the condition ofthe base metal and over the cladding process itself. The absence ofsurface oxides, contaminants and the like is a critical factor inobtaining the desired adherence between the base metal and theprotecting metal to be clad thereon. Especially, brittle intermetalliccompounds of compatible metals and thermal stress pose problems in thismechanism.

The mechanical cladding technique to achieve a metallurgical bondbetween two pieces of metal by deforming the two materials also hassimilar disadvantages. In this technique, it is very hard to achieve anintimate bond between the cladding material and the base metal. Forexample, the residual stress produced by rolling work is prone todeteriorate the bond between the two materials.

Although explosives have been used for several centuries and metals havebeen welded by various techniques for many more centuries, it has beenonly recently that explosives have been used to perform welding. Strongmetallurgical bonds can now be produced over metal combinations whichcannot be welded by other methods.

Explosive welding (bonding) is carried out by bringing together properlyprepared metal surfaces with a high relative velocity, high pressure,and proper orientation, so that a large amount of plastic interactionoc-' curs between the surfaces. The dynamics of this highvelocitycollision are extremely complex. Only in the.

last few years have instances of explosive bonding been reported in theliterature by numerous workers and in trade journals. Betterquantitative relationships are now being developed to predict morereliably the results of explosive welding operations. Until suchconfident control of the process is achieved practical applications willcontinue to depend upon empirical knowledge and experience, or uponrigidly standardized welding operations using special explosivechargecomponents or explosive welding machines.

The present state of the art of explosive welding techniques allowsproduction of uniform flat clad plate of unique metal combinations andproperties. In fact, commercial size clad plates are now being producedand marketed, and many companies in the world are currently developingnew products for commercial application.

Although cladding techniques for flat plates have been well developedand the flat clad plates are commercially available, cladding on ageometrically nonuniform base plate has not been accomplishedsuccessfully. The effects on the mechanics of explosive bonding of ageometrically non-uniform surface and of the variation in direction ofexplosive detonation on a nonuniform surface have also not beendetermined.

It is, therefore, an object of this invention to provide a solution tothe technical problems involved in the above-mentioned cladding methods.

A second object is to provide a method of achieving a metallurgical bondbetween two pieces of metal by use of explosives.

A third object is to provide an explosive cladding method for commercialapplications on a broad scale.

A fourth object is to provide a method of achieving a metallurgical bondbetween two pieces of metal having geometrically non-uniform ornon-linear surfaces.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages are realized and attained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an example of a preferredembodiment of the invention and together with the description serve toexplain the principles of the invention.

In the drawings:

FIG. 1 is a schematic illustration of an arrangement of explosivecladding embodied in this invention;

FIG. 2 shows the relationship of the important process variables forexplosive bonding with a lowdetonation-velocity explosive observed inthe invention; and

FIGS. 30 3d illustrate the mechanism of explosive cladding as embodiedin this invention.

In order to accomplish the objects of this invention, a metallurgicalbond between two pieces of metal can be achieved by use of the energydeveloped by an explosive of proper detonating rate or velocity tocollide mating metal surfaces with each other. In general, this processof bonding is achieved by placing the base metal at a fixed locationwhich is kept at a certain distance from the position of the claddingmaterial and by detonating the explosive loaded on the claddingmaterial.

In order to achieve the metallurgical bond between the cladding materialand the base metal, as embodied in this invention, it is necessary tobring atoms of the cladding material sufficiently close to atoms of thebase metal so that their normal forces of interatomic attraction may actto produce a bond. However, the surfaces of metal and alloys often arecovered naturally with films of oxides, nitrides and absorbed gases, andin the presence of such films or coatings, mating metal surfaces willnot bond even under a very high pressure. Removal or effacement ofinterrupting surface films is, therefore, necessary to achieve thedesired bond.

In the present invention, it has been observed that the dynamic anglebetween the colliding surfaces must be maintained within criticallimits, as a result of properly controlled explosive-bonding parameters,to make a jet, or a portion of the colliding surfaces, which is expelledso as to achieve a metallurgical bond. The unwanted films on collidingsurfaces are removed or broken up because of severe deformation andextension of the colliding surfaces and the resulting jet, and film-freesurfaces remain and are pressed into intimate contact so that the matingsurfaces can be metallurgically bonded.

It has been also observed in the invention that the collision velocityand detonation velocity have a great influence on the bonding process.In a collision between two pieces of metal, pressure disturbances aredeveloped and propagated, and their types are dependent on the collisionvelocity and the detonation velocity.

When the collision velocity Vc exceeds the sonic velocity Vs of thecladding material, attached shock waves at the collision point C aregenerated into each metal, as illustrated in FIG. 3a. The shock frontmoves with the collision point and subjects the atoms to high pressures.These pressures are dependent on the collision velocity and physicalproperties of the metal. However, when expansion waves, which originateat the outer surfaces, reach the interface, they destroy the highpressure waves, causing the metal to separate.

If the collision velocity is approximately equal to the sonic velocity,the shock waves become detached and move ahead of the collision point.Detached shock waves are also formed when the collision angle B exceedssome critical values at a given collision velocity, and the criticalangle is proportional to the detonation velocity.

When the collision velocity is less than the sonic velocity of thecladding material, no shock waves appear, since the pressure is spreadahead of the collision point as shown in FIG, 3c.

If the pressure ahead of the collision point, as in the cases ofdetached and non-shock waves, is great enough to cause plasticdeformation of both metal surfaces, a flow of metal in the form of a jetwill be initiated to remove or break up the unwanted films on thecolliding surfaces, with the result that the mating metal surfaces aresubjected to great pressures to achieve a metallurgical bond.

The proper detonation velocity as developed in the example of thisinvention is approximately l0,000 feet/sec. If the velocity exceedsexcessively this limit, the velocity at the collision point will belarger than the sonic velocity of the cladding material to generateshock waves with no resulting jet, as described above, and if thevelocity is less than the limit, pressures will decrease to fail inachieving good bonding.

In this invention, an empirical relationship developed by the BattelleMemorial Institute of U. S. A. was used that relates the identifiedmaterial and process variables to the quality of explosive bonding. Thiswas developed in terms of an energy-balance method during theexperimental work at Battelle Memorial Institute.

The relationship is as follows: La(tpo'y)/d where L weight of explosiveper unit area of cladding plate t= cladding plate thickness p claddingplate density o'y cladding plate yield strength d interface gap(standoff distance) Using this relationship as a guide, different valuesof the factor (tp0y)/d were selected and tried with different values ofL to establish limits on the value of L which would give good bonding.This effort resulted in a successful graphical relationship by plottingthe explosive loading L against the factor (tp 'y)/d, as illustrated inFIG. 2. This graph is valid only for a particular explosive; in thiscase, anon-nitroglycerine dynamite, T7OC, a product of the Trojan PowderCompany,

- was used at a vibratory-packed density of 1.0g/cc, and

it had a detonation velocity of approximately 10,000 feet per second.This graph can normally be used to determine either the standoffdistance or explosive loading for particular values of o'y,p and t.-

For the-experiment in this invention, T7OC explosive was used, asdescribed above, and the explosive loading L was determined with thefollowing values of 0'y,p,t and d.

o'y 56,000 psi p 6.286 lb/in t= V8 in d A; in

As a result of calculation for L, a value of approximately 9 grams perin was obtained.

As a result of this invention, cladding on various nonlinear metalplates is now possible. (Zommercialsize clad plates of stainless steel,carbon steel and titanium steel, etc., have been produced for use inexplosive methods. Also, the cylindrical explosive cladding techniquehas been applied in welding tubes and tube plates of heat exchangers.However, the explosive cladding techniques developed hitherto arelimited to flat plates and cylinders where the explosive detonationfront moves in a linear direction. However, the method embodied in thisinvention can apply explosive cladding on a broader scale and includesexplosive cladding when the explosive detonation front moves'in anon-linear manner.

As illustrated in FIG. 1, a base metal 5 is so placed as to maintain acertain distance 6 (standoff distance) from a cladding material 4, whichhas a certain thickness. A buffer material 3 is laid on the claddingmaterial -to protect the surface of the cladding material from harmfulexplosion products and to prevent cracking of the cladding material dueto thermal stress. An explosive 2, with a detonation velocity ofapproximately l0,000 ft/sec, is spread out in a certain density on thebuffer material. The required density value of explosive can be obtainedfrom the factor (tprry )/d and FIG. 2. The distance between bendingknots 7 is determined by the formula ofl= d tan 0/2 where I= distancebetween bending knots of base metal and cladding material a standoffdistance between cladding metal and base metal 0 bending angle in orderto maintain a constant standoff distance.

After all the necessary components are arranged as described above, adetonator l is detonated to blast the explosive. Approximately half ofthe energy generated in the explosive detonation is propagated to thecladding material through the buffer material to bend the claddingmaterial in a certain slope so as to collide with the base metal at avery high velocity to achieve explosive bonding according to themechanisms described above. When the explosive detonation front moves tothe bending portion, the direction of detonation front changes to makethe detonation unstable but the detonation direction is soon normalizedto achieve good explosive cladding.

Although in the experiment of this invention specimens were so arrangedas to make the direction of explosive detonation front change twice, thedirection can change several times, and explosive cladding can be madeas satisfactorily on non-linear behavior plates as well as on flatplates. The direction of detonation can be as shown in FIG. 1, e.g.,down the slope or it can be in the opposite direction, up the slope.Either direction of detonation provides the desired bonding.

This invention is not limited to the conditions and requirementsdescribed above; it can be so modified within the scope of the methods,which are claimed in this invention, as to be made applicable to variousconditions and requirements depending on the situation.

What is claimed is: l. A method of explosively cladding one non-linearlyshaped metal upon another non-linearly shaped metal, comprising thesteps of:

providing a metal base member, having a non-linear shape formed by atleast two planar surfaces to be explosively clad, including a firstplanar surface at an angle to and joined with a second planar surfaceand forming a first bending knot at the point where the two planarsurfaces meet, and positioning said metal base member in a fixedlocation; placing a metal cladding plate, having a non-linear shapesimilar in shape to the non-linear shape of said base member, and formedby at least two planar surfaces including a third planar surface joinedwith a fourth planar surface at a second bending knot, said third andfourth planar surfaces having the same angle as said first and secondlinear surfaces, a selected distance away from the base member in afirst direction, said first and third surfaces being adjacent oneanother and separated by an interface gap equal to said selecteddistance;

positioning a buffer material on the cladding plate with said claddingplate located between the metal base and the buffer material;

placing a predetermined amount of explosive on the buffer material sothat the explosive changes its shape and corresponds to the shape of thebase member that is to be cladded;

igniting the explosive to cause the explosive to burn at a predetermineddetonation velocity and to change its explosive front in accordance withthe shape of the base member that is to be cladded;

forcing said planar surfaces of the base member and of the claddingplate together at a selected collision velocity", and

plastically deforming said planar surfaces to create a flow of metalbetween the surfaces in the form of a jet to remove or break up anyunwanted films upon collision of the planar surfaces whereby thesurfaces are subjected to great pressures to achieve a metallurgicalbond between the base member and the cladding plate.

2. A method as in claim 1 wherein said first bending knot of the basemember and said second bending knot of the cladding plate are spacedfrom each other in a second direction perpendicular to said firstdirection, and the distance in said second direction is determined bythe formula of l =d tan 0/2 where I distance in said second directionbetween said first and second bending knots of the base member and thecladding plate d distance of the interface gap between the base memberand the cladding plate, and

0 bending angle between said first and second planar surfaces andbetween said third and fourth planar surfaces.

3. A method as in claim 1 wherein the predetermined amount of explosiveused is determined by the following formula ofLa(tpa'y)/d where L weightof explosive per unit area of cladding plate t= cladding plate thicknessp cladding plate density (7 =,cladding plate yield strength and dinterface gap (standoff distance) 4. A method as in claim 3 wherein thecollision velocity is equal to or less than the sonic velocity of thecladding plate material.

5. A method as in claim 4 wherein the detonation velocity of theexplosive is no greater than 10,000 feet per second. 7

6. A method as in claim 1, wherein said base member includes a fifthplanar surface joined to said second planar surface at a third bendingknot and parallel with said first planar surface, and said claddingplate includes a sixth planar surface joined to said fourth planarsurface at a bending knot and parallel tosaid third planar surface.

7. A method as in claim 6 wherein said first bending knot of the basemember and said second bending knot of the cladding plate are spacedfrom each other in a second direction perpendicular to said firstdirection, and the distance in said second direction is determined bythe formula ofl=d tan 0/2 where l= distance in said second directionbetween said first and second bending knots of the base member and thecladding plate d distance of the interface gap between the base memberand the cladding plate, and 0 bending angle between said first andsecond planar surfaces and between said third and fourth planarsurfaces, and said third and fourth bending knots are spaced from eachother in said second direction at a distance equal to the distance 1between said first and second bending knots.

where L weight of explosive per unit area of cladding plate t claddingplate thickness p cladding plate density 0 cladding plate yield strengthand d interface gap (standoff distance).

1. A method of explosively cladding one non-linearly shaped metal uponanother non-linearly shaped metal, comprising the steps of: providing ametal base member, having a non-linear shape formed by at least twoplanar surfaces to be explosively clad, including a first planar surfaceat an angle to and joined with a second planar surface and forming afirst bending knot at the point where the two planar surfaces meet, andpositioning said metal base member in a fixed location; placing a metalcladding plate, having a non-linear shape similar in shape to thenon-linear shape of said base member, and formed by at least two planarsurfaces including a third planar surface joined with a fourth planarsurface at a second bending knot, said third and fourth planar surfaceshaving the same angle as said first and second linear surfaces, aselected distance away from the base member in a first direction, saidfirst and third surfaces being adjacent one another and separated by aninterface gap equal to said selected distance; positioning a buffermaterial on the cladding plate with said cladding plate located betweenthe metal base and the buffer material; placing a predetermined amountof explosive on the buffer material so that the explosive changes itsshape and corresponds to the shape of the base member that is to becladded; igniting the explosive to cause the explosive to burn at apredetermined detonation velocity and to change its explosive front inaccordance with the shape of the base member that is to be cladded;forcing said planar surfaces of the base member and of the claddingplate together at a selected collision velocity; and plasticallydeforming said planar surfaces to create a flow of metal between thesurfaces in the form of a jet to remove or break up any unwanted filmsupon collision of the planar surfaces whereby the surfaces are subjectedto great pressures to achieve a metallurgical bond between the basemember and the cladding plate.
 2. A method as in claim 1 wherein saidfirst bending knot of the base member and said second bending knot ofthe cladding plate are spaced from each other in a second directionperpendicular to said first direction, and the distance in said seconddirection is determined by the formula of l d tan theta /2 where ldistance in said second direction between said first and second bendingknots of the base member and the cladding plate d distance of theinterface gap between the base member and the cladding plate, and thetabending angle between said first and second planar surfaces and betweensaid third and fourth planar surfaces.
 3. A method as in claim 1 whereinthe predetermined amount of explosive used is determined by thefollowing formula of L (t Rho sigma y)/d where L weight of explosive perunit area of cladding plate t cladding plate thickness Rho claddingplate density sigma y cladding plate yield strength and d interface gap(standoff distance)
 4. A method as in claim 3 wherein the collisionvelocity is equal to or less than the sonic velocity of the claddingplate material.
 5. A method as in claim 4 wherein the detonationvelocity of the explosive is no greater than 10,000 feet per second. 6.A method as in claim 1, wherein said base member includes a fifth planarsurface joined to said second planar surface at a third bending knot andparallel with said first planar surface, and said cladding plateincludes a sixth planar surface joined to said fourth planar surface ata bending knot and parallel to said third planar surface.
 7. A method asin claim 6 wherein said first bending knot of the base member and saidsecond bending knot of the cladding plate are spaced from each other ina second direction perpendicular to said first direction, and thedistance in said seconD direction is determined by the formula of l dtan theta /2 where l distance in said second direction between saidfirst and second bending knots of the base member and the cladding plated distance of the interface gap between the base member and the claddingplate, and theta bending angle between said first and second planarsurfaces and between said third and fourth planar surfaces, and saidthird and fourth bending knots are spaced from each other in said seconddirection at a distance equal to the distance l between said first andsecond bending knots.
 8. A method as in claim 1 wherein the collisionvelocity is equal to or less than the sonic velocity of the claddingplate material.
 9. A method as in claim 8 wherein the detonationvelocity of the explosive is no greater than 10,000 feet per second. 10.A method as in claim 9 wherein the predetermined amount of explosiveused is determined by the following formula of L (t Rho sigma y1d whereL weight of explosive per unit area of cladding plate t cladding platethickness Rho cladding plate density sigma y cladding plate yieldstrength and d interface gap (standoff distance).